Nodes, such as wireless sensor nodes, are often battery operated. In some applications, a battery may be required to power a node for a long time (e.g., years). Moreover, the node may be located in a place where access is limited, making battery replacement difficult and expensive.
Nodes are often powered by batteries that are based on lithium technology. Such batteries have a very flat voltage discharge curve, making accurate sensing of the battery's remaining energy difficult. Coulomb counters can be used to directly track energy drain from the battery. However, coulomb counters consume too much energy and are impractical in applications where limited battery capacity is available and where long service life is needed.